Electron beam lithography is a process used in microelectronics fabrication technology for the generation of very small features and patterns which eventually become electrical devices and circuits. Pattern definition results from the interaction of a fine beam of electrons with an electron beam resist which alters the solubility properties of the electron beam exposed areas. Development of the desired pattern is normally accomplished with organic solvents. Typical resist compositions used in the lithographic process are organic polymers owing to their ability to undergo molecular cross-linking (negative resist) or chain-scission (positive resist) during electron irradiation. As a consequence of the resist's insulating properties, charge build-up occurs upon electron beam exposure. This "charging effect" is detrimental since it may cause defocussing of the incident electron beam with a subsequent loss in pattern resolution. In order to circumvent this problem, it is necessary to dissipate or neutralize the excess charges. In the prior art, charge dissipation has been described often as being effected by applying a thin conducting film either on top of or below the resist layer. Such as described, for example, in U.S. Pat. No. 3,940,507. This operation is described also in Electron-Beam Technology, A. R. Brewer, Academic Press, New York, 1980, pp. 226-227. Specimen clamps are used to provide a discharge path to ground. Typically, gold or aluminum at a thickness of a few hundred angstroms is employed. Before development of the pattern, this metallic film must be removed.
The deposition of the metallic film is generally accomplished by evaporation or sputtering of an appropriate target. Whether the conductive film is placed above or below the resist layer, transport of the processed sample from the resist coater to the metal deposition chamber (or vice versa) is necessary. This extra handling step is detrimental to good yields. Moreover, removal of the metallic film may involve chemicals not normally used in semiconducting processing; thus, contributing to an additional source of contamination.
The problem of electrostatic charging also exists for ion implantation of dopants (e.g. boron or phosphorus). However, in this case positive charges are deposited into the sample. Due to the electrical imbalance resulting from this charge accumulation, electron conduction is necessary in order to maintain neutrality. If this is not possible due to the insulating properties of the substrate, a net electrical potential is obtained which, as in electron beam lithography, results in good resolution limitations and alterations of MOS gate electrical properties and performance.
Accordingly, a need exists for a technique that obviates the disadvantages attendant in the dissipation of charges build up from electron beam exposures in semiconductor manufacture and/or a procedure that reduces the accumulation of electrostatic charges.